Service Manual

Virtual Router Redundancy Protocol

(VRRP)

Virtual router redundancy protocol (VRRP) is designed to eliminate a single point of failure in a statically

routed network.

VRRP Overview

VRRP is designed to eliminate a single point of failure in a statically routed network.

VRRP specifies a MASTER router that owns the next hop IP and MAC address for end stations on a local

area network (LAN). The MASTER router is chosen from the virtual routers by an election process and

forwards packets sent to the next hop IP address. If the MASTER router fails, VRRP begins the election

process to choose a new MASTER router and that new MASTER continues routing traffic.

VRRP uses the virtual router identifier (VRID) to identify each virtual router configured. The IP address of

the MASTER router is used as the next hop address for all end stations on the LAN. The other routers the

IP addresses represent are BACKUP routers.

VRRP packets are transmitted with the virtual router MAC address as the source MAC address. The MAC

address is in the following format: 00-00-5E-00-01-{VRID}. The first three octets are unchangeable. The

next two octets (00-01) indicate the address block assigned to the VRRP protocol, and are unchangeable.

The final octet changes depending on the VRRP virtual router identifier and allows for up to 255 VRRP

routers on a network.

The following example shows a typical network configuration using VRRP. Instead of configuring the

hosts on the network 10.10.10.0 with the IP address of either Router A or Router B as their default router;

their default router is the IP address configured on the virtual router. When any host on the LAN segment

wants to access the Internet, it sends packets to the IP address of the virtual router.

In the following example, Router A is configured as the MASTER router. It is configured with the IP

address of the virtual router and sends any packets addressed to the virtual router through interface

TenGigabitEthernet 1/1 to the Internet. As the BACKUP router, Router B is also configured with the IP

address of the virtual router. If, for any reason, Router A becomes unavailable, VRRP elects a new MASTER

Router. Router B assumes the duties of Router A and becomes the MASTER router. At that time, Router B

responds to the packets sent to the virtual IP address.

All workstations continue to use the IP address of the virtual router to address packets destined to the

Internet. Router B receives and forwards them on interface TenGigabitEthernet 10/1. Until Router A

resumes operation, VRRP allows Router B to provide uninterrupted service to the users on the LAN

segment accessing the Internet.

For more detailed information about VRRP, refer to RFC 2338, Virtual Router Redundancy Protocol.

Virtual Router Redundancy Protocol (VRRP)

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